Fabrication of support-module



Aug. H, 1970 c. BICKOFF T v FABRICATION 0F SUPPORT-MODULE 5 Sheets-Sheet 1 B 6 9 1 9m m a J 6 e 1 1 F PRIOR ART FIG. 2D

A v mmmmkm STRAIN Fl 6. 3

lNVENTOR. CHARLES BICKOFF ATTORNEY Aug. 11, 1970 c. BICKOFF msmcurxou 0F surron'r-uonum 3 Sheets-Sheet 2 Filed Jan. 2. 1 968 FIG. 2A

SL-l

SL-l

INVENTOR. CHARLES BICKOFF ATTORNEY Aug. 11, 1970 c. BICKOFF 3,523, 92

FABRICATION 0F SUPPORT-MODULE Filed Jan. 2, 1968 5 Sheets-Sheet 5 INVENTOR. CHARLES BICKOFF ATTORNEY United States Patent 3,523,992 FABRICATION OF SUPPORT-MODULE Charles Bickolf, Quincy, Mass., assignor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware Filed Jan. 2, 1968, Ser. No. 695,178 Int. Cl. B29c 24/00; B29d 3/02; B41j 11/00 US. Cl. 264-463 13 Claims ABSTRACT OF THE DISCLOSURE A method of fabricating a set of glass fiber resin supports, and especially a set of paired-supports, for a carefully aligned array of print-hammers whereby, in one embodiment, a set of support strip pairs is laid up in a form, each pair in operative relation with an associated hammer slug, each strip being indexed with an associated cavity in the respective slug, these slugs being aligned in the form so these cavities are in registry for injection of potting material through each set of so-registered cavities, the form also being provided with break-away separator slugs, each being removably placed between adjacent hammers for maintaining a prescribed separation thereof, these slugs including cavity means registering with the registered hammer-cavities and also being adapted to be shifted before the cavity potting has completely set up to thereby separate each hammer-support mount for independent hammer pivoting.

PROBLEMS, INVENTION FEATURES Flexure mounts for supporting a number of print-hammers from a common base are well-known in the art, for instance, as adapted for use in high-speed printers associated with data processing systems. Hammer unit HU in FIG. 1 is schematically representative of such (more details may be found in US. 3,334,409 to Schneider et al.). As workers in the art well know, the task of joining such supports to the relatively rigid base and hammerslugs, such as to satisfactorily operate over the long-duty cycle and under the extreme acceleration etc. conditions of high-speed printers is one of the most challenging in the printer arts. One reason is the common and rather exasperating tendency of such slug-supports to wander out of alignment with one another either during fabrication or thereafter during operation. Of course, this tendency can readily lead to printing misalignment, something intolerable in typical high-quality, high-speed printout today. This problem is discussed, along with various different solutions, in co-pending application U.S. Ser. No. 575,443 to Braxton, filed Aug. 26, 1966 (herewith incorporated by reference). This support-registration problem is a severe one and can result, for instance, from a poor support-bond (to the slug, to the base or to both) whereby actuation of the print-slug may cause them to impact misaligned, to interfere with an adjacent slug, etc., resulting in clipped" characters and other like hallmarks of poor print quality. It is recognized that a primary cause of this stems from defective print-hammer fabrication, e.g., in the method and materials used in assembly; for instance, the materials (such as spring steel) typically used for prior art support-fiexures are prone to exhibit certain structural weaknesses, some deriving from treatment received during manufacturing and/ or handling. One such weakness is notch-sensitivity whereby any slight surface discontinuity (such as an edge-notching caused during the stamping-out of such a steel support, or a scratching of the surface by the operator, such as with a trimming knife during the potting operations) can very quickly lead to support-rupture and failure (these notches soon propagating a crack or tear and rupturing). The

invention teaches a method of fabricating print-hammer modules of certain superior two-phase (composite) materials using a jig for aligning hammer-slug support units in prescribed registry and keeping them so during potting; this technique involving no operations with scratch hazards (e.g., no trimming knives, etc.); and using material which is not notch sensitive.

In addition to the aforementioned disadvantages, prior arthammer fabrication techniques are also undesirably slow, fussy and not readily adaptable to foolproof (e.g., automated) assembly. Because of the aforementioned registration difficulties, prior art techniques are not practical for more than a few (e.g., two) hammers in a module (since the buildup of registration-variances quickly becomes intolerable from hammer to hammer). Moreover, there are all too many individual steps, most requiring the intervention of a human operative, such as for bonding and positioning the supports relative to the base and relative to the slugs, as well as for the trimming of this bond, etc. The present invention eliminates the aforementioned difficulties and disadvantages by eliminating these individual steps and blending them all into a single integral operation using a multifunction jig, by eliminating operator treatments which are likely to injure the module or which require special skill (e.g., to maintain registration, to trim, etc.) and by easily maintaining errorfree hammer registration over the span of several hammers in a large set (e.g., up to about 12). As a result, methods employing the invention may be expected to produce hammer modules with as many as 12 hammers at the same cost, or less, as conventional two-harnmer modules. Moreover, because of the high quality materials and precision of assembly, it has been found that hammer modules fabricated according to the invention have a failure-free lifeat least treble that of conventional modules under typical life-test conditions.

Workers in the art will recall many problems associated with typical prior art fabrication techniques, such as for building and assembling print-hammer modules like that of the aforementioned Schneider patent. Reflection upon these techniques will better illustrate the advantages and benefits accruing from the fabrication of hammer modules according to the invention. Thus, typical prior art fabrication will involve such steps as: separately shaping each support (flexure), trimming, priming and inspecting them; separately bonding a pair of those flexures to a respective hammer slug whlie maintaining registry, then inspecting; then bonding each such pair of slug-attached flexures to a respective base while maintaining registry (difficult since misalignment commonly results, e.g., from handling, stresses in bonding agent, etc.), then inspecting, trimming, loading and separating the bonding fixtures; finally discarding reject modules and assembling a set of them in a print-hammer assembly while maintaining very precise relative alignment (this last being a very critical, yet fussy procedure; often introducing errors). The invention, of course, eliminates all of the foregoing steps and their attendant costs, their inconvenience, and most importantly, the defects and errors that they are prone to introduce.

PRIOR ART EXAMPLE In the art of designing high-speed printers, such as for providing computer printout, it is conventional today to mount the print-hammers as indicated in FIG. 1 where a double print-hammer unit HU is shown somewhat schematically. It will be understood that a plurality of such units is typically arrayed across a printing zone to be operatively adjacent the locus of the print drum and intermediate paper and ribbon material, e.g., such units for a -column printer. Each such unit HU will generally comprise a pair of hammers (slugs) S1, -2, each mounted, front and rear, on a pair of pivot flexures f in prescribed relation to a fixed base BB; the base being adapted to be located in prescribed relation with the printing locus, as known in the art. Flexure supports 1 are typically joined to their respective slugs S by an elastomeric (or like) bond bd embedded in a cavity in the slug and are similarly bonded to base BB through a similar bond bd embedded in cavities therein. Such a module may be about 1 /2 in. high (slugs S being about 1 /2 in. long, about in. wide and separated by only a few mils). Such flexures 7'" support the hammer load to be pivotable in a prescribed (print-impact) direction, while storing and releasing energy under high frequency printimpacting. Thus, as understood in the art, when hammer unit HU and its companion units are properly fixed and aligned along their printing locus, they will be adapted to be impacted (launched) at their tail portion, St, to drive their print-impacting nose portion, S-n, against the print drum and intermediate forms (as indicated by the arrows). This operation is recognized as imposing high impact, high frequency stresses on these units to the extent that failure of hammer units, and especially of their flexure supports, is perhaps probably the most common and troublesome malady in todays high-speed printers. Moreover, this problem exists despite the fussy, expensive fabrication operations typically employed (as aforementioned) to make the hammer units so they will respond quickly enough, will apply a constant impact force, and will keep properly aligned and not fail under hundreds of millions of high-stress cycles. This is a uniquely-severe flexure environment; no other within contemplation demands such extremely long (high-frequency) cycle-life.

As workers in the art well know, the joining of the support flexures f to relatively rigid base BB, as well as to slugs S, involves many disagreeable problems. One such problem is maintaining a precise orientation of the slugs relative base BB (so that it may be operatively driven in precise alignment against the paper-something critically important for high-speed printers, of course). Such problems have called forth fabrication procedures which are all too complicated, such as arranging the hammer parts in a jig, pouring and molding settable bonding material around them and thereafter curing, etc.all the while trying to keep them precisely aligned despite curing stresses, shrinkage and the like. It is well-known that such procedures characteristically make it a genuine feat to keep these parts aligned; especially since the bonding materials can, themselves, introduce distortion (e.g., from shrinkage between the flexure and the bonded member). This problem is greatly amplified, of course, by stresses resulting from manually handling of the units, as is necessary with conventional fabrication methods. The present invention provides a novel hammer-module and associated fabrication technique involving none of the above problems and providing superior operating characteristics, as well as more fabrication convenience and reliability.

Another difficulty associated with bonding slugs to their supports is that of support-fatigue and breakage. With high-speed printers using the flexure strips f of FIG. 1, for instance, this is an outstanding problem, given the typical extreme slug-actuating forces and high frequency operation. Unless this actuation is quite precisely controlled and over a very long life, the units will not serve satisfactorily with high-speed computer systems. Moreover, such units are uneconomic unless they can be made to be virtually 100% reliable and maintenance-free, since their failure will typically shut down an expensive computer system costing hundreds of dollars per hour. The present invention will be seen to provide an answer to these difficulties in providing a highly reliable mounting arrangement for hammer-slugs and for bonding these in place so as to give improved operation and reliability over a longer life. More particularly, the invention provides such an advantageous mount in the form of a multislug integrally-molded module.

The aforementioned prior art problem of support fatigue and breakage stems, to a great extent, from the materials and fabrication methods heretofore used in fabricating the flexures 1 (FIG. 1). For instance, flexures f are customarily stamped from stock spring steel and thus are especially apt to be notch-sensitive; that is, apt to have tiny irregularities along their edges which act as failure sites liable to induce premature rupture and failure. This problem can be somewhat ameliorated by grinding such edges to be very smooth; however, this is an expensive, fussy procedure and is best avoided, if possible. More importantly, the techniques for fabricating conventional hammer modules, such as that of FIG. I typically involve hazardous operator handling and treatments, especially in the bonding area, as aforementioned. That is, the fabrication of such modules typically involves an operator trimming, scraping, etc., the bonding areas, such as the polyurethane fillets, cf bonds bd, bd in FIG. 1. During such treatments, it is recognized that all too often an operator can cut and scrape the bond (e.g., knife slip While trimming), can injure the flexures f, such as by scratching them, bending (permanently deforming) them, etc. By contrast, the invention eliminates all such hazards and problems and makes the module cheaper and more convenient to fabricate according to a one-step multislug bonding technique whereby the bond is made automatically without intervention of the operator.

Thus, it is one object of the invention to provide improved mounting assemblies for print-hammers and the like, and improved associated fabrication methods, and to alleviate problems like the foregoing. A related object is to provide such methods with an improved technique for bonding composite flexure strip supports to hammer slugs and the like. Yet, a further related object is to provide a more specific technique for bonding a plurality of aligned such strips to an associated array of print-hammer slugs.

Still another object is to provide a technique for fabricating such assemblies in a manner which eliminates operator handling and treatments likely to damage the unit. A related object is to eliminate the risk of notch-sensitivity and similar problems. Yet another object is to provide such assemblies by a technique which extends their reliable operating life substantially. Another object is to fabricate such assemblies at lower cost per failure-free operating hour. Still another object is to provide such assemblies by a method which allows the reliable mounting of more than two hammer slugs from a common base module. Another important object is to provide such an assembly technique whereby slug registration is assured more reliably. A more particular object is to provide a fabrication technique whereby the slug-support is provided with greater contact area in relation to the slug for bonding therewith. Still a more particular object is to provide an improved method of supporting a plurality of hammer-slugs from a common base module with glass fiber resin strips.

The above and other related features, objects and advantages are achieved according to one embodiment of the invention by a fabrication implement arranged to array a prescribed set of hammenslugs in prescribed registration along a reference plane; to thereafter align two sets of glass fiber resin, slug-supporting strips in registry with two prescribed sets of bonding cavities in each respective one of these slugs, each strip being disposed for registry with a particular cavity, each set of cavities being in registry for introduction of a bonding resin therein as a set; next, introducing this resin, in common, along each set of cavities (and along at least a bonding portion of the common base); and thereafter thrusting separation means along this reference plane and between each set of slug-cavities to separate the bonding resin therein and allow independent operation of each slug as known in the art.

Further objects and features of the present invention may become apparent upon consideration of the following detailed description of certain embodiments thereof, especially when taken in conjunction with the accompanying drawings wherein like reference characters denote like parts and wherein:

FIG. 1 is an upper isometric view of a two-slug printhammer unit constructed according to prior art techniques and adapted for incorporation in a high-speed printer;

FIGS. 2C and 2A illustrate preliminary and intermediate steps, respectively, in fabricating a multislug print-hammer module according to one technique embodiment of the invention, FIG. 2B indicating the sofabricated module; while FIG. 2D shows, in plan view, a mold form for providing sets of strips as indicated in FIG. 2C;

FIG. 3 represents a somewhat idealized set of stress/ strain curves illustrating the characteristics of support material adapted for use in the invention;

FIG. 4 is a side-isometric, idealized view (not-to-scale) of a preferred slug-support construction; and

FIG. 5 is an upper isometric view of a six-slug hammer module fabricated according to an alternate form of the invention.

GENERAL MATERIAL CHARACTERISTICS I have found that it is especially advantageous to fabricate hammer (slug) supports to be of compositematerials having diverse elastic characteristics. Preferably, they comprise several layers of strong, high-modulus filaments (such as glass fiber strands) potted in a relatively weak, more elastic potting (binding) matrix (such as a compatible resin strongly adherent to the glass). I have found that such a composite construction of diverse-elasticity materials can provide a mounting flexure at reasonable cost having strength and elasticity properties that no analogous homogeneous (single-phase) material appears to possess. For instance, glass fiber resin strips yield a support flexure that is unexpectedly advantageous. It appears best that the bulk of this material comprise the high strength (glass fiber) material, dispersing the elastic matrix material (resin) adherently therebetween. The resultant composite structure is able to absorb a loading stress that would easily rupture the weaker plastic (if used alone); while dispersing the high strength fibers throughout this matrix and isolating them somewhat this way, prevents minor imperfections in any single fiber from being propagated across the entire structure. As a result, While individual filaments may yield to an applied load, the load will thereupon be redistributed through the elastic matrix to be borne by other filaments in the composite structure. It has been found that the filament material must be considerably stronger than the matrix material, as explained hereinafter.

The aforementioned glass fiber plastic material comprises a web support structure for mounting the hammer slugs (or like reciprocating elements). In a general sense, such a composite structure may be thought of simply as an array of parallel fibers (layers of) aligned primarily along a particular stress direction and comprising the bulk of the flexure support, being embedded in a minor portion of relatively resilient bonding material as a matrix. Such fibers may be either natural or manmade, may be of organic, inorganic or metallic material, and may comprise one continuous filament or discontinuous filaments, each filament comprising an individual fiber, a yarn, a yarnbundle, etc. The matrix or binder material may, in general, be organic or inorganic (e.g., metallic) and can be made soft or hard, brittle or tough, conductive (elec. or thermal) or not; and resistant; to weather, to heat, to chemical corrosion and to moisture, as the application demands. Of course, as aforestated, the preferred structure is glass fiber filaments embedded in a thermosetting resin.

While the technical explanation behind the operation of such a two-phase slug support is not yet fully known, a great deal has been learned. As a general summary, the following characteristics may be noted. A fundamental assumption will be that the strong and wea (fibrous and matrix) materials can act together as a unit (e.g., like a monolithic cantilever beam) and can be made to stretch, compress, twist, etc., under applied stress loads to a similar degree, so that both are distorted similarly. To achieve this action, the following conditions should obtain:

(1) The fibers all be essentially straight and (mostly) aligned in a common direction (direction of expected loading);

(2) The fibers must be arranged to be stressed to relatively the same degree;

(3) A good bond must exist between the matrix and the fibers and, although this bond need not be continuous, the bonding points must be close enough together to ensure that the two disparate materials can absorb strain unitarily. The key function of the bond is to transfer the load to the fibers, such as by preventing any appreciable slippage of the fibers, misalignment with loading direction, etc. and

(4) The composite structure must be used only in the proportional stress/strain operating region (i.e., obey Hookes law); that is, given an applied stress, the strain (elongation per unit length) of each material will be proportional to the stress it assumes.

While the foregoing may generally indicate the materials to be used in assemblies made according to the invention, reference is made to a copending, commonly-assigned US pat. application, Ser. No. 669,216 to Schneider, filed Sept. 20, 1967, and now Pat. No. 3,447,455, wherein this is particularized more, specifying the characteristics of the desired composite materials generally and of glass fiber resin materials particularly, giving examples of each material and further specifying the operating stress characteristics desired in a hammer-slug support structure in general. The references to material elasticity, above and as follows, may be clarified by reference to the stress/ strain curves (idealized) in FIG. 3. Here, curve E suggests the proportional (Hooke) re lationship, or elastic modulus E (e.g., B/a). A second curve indicates the performance of an idealized matrix material beyond the elastic threshold (E i.e., the limit beyond which no more stress can be borne and virtually infinite deformation (or rupture) occurs; thus representing the Weaker, more elastic material. The other curve indicates the elongation (stretchability) modulus E for a typical filament material (such as glass fiber having a relatively high stress value level (C or over) for a particular strain or deformation, as opposed to that of the Weaker matrix material (such as level B for curve E A prescribed failure point is FP, also indicated for this filament material, beyond which elasticity is not proportional (FP being the proportional limit beyond which Hookes law does not apply).

FABRICATION METHOD According to one embodiment of the fabrication method indicated in FIGS. 2A, 2B, 2C and 2D, a 12- slug (l2-column) print-hammer module HM is to be fabricated, this being understood as representative of how the invention is uniquely apt for such multi-support module fabrication. Modules like HM will be recognized as useful in the art, for instance, being modular for the common 96-column, 108-column, etc., printing configurations. Here, as best indicated in FIG. 2C, a set SH of 12 U-shaped slug-supporting strips (set SH comprising strips C-l, C-2 through C-12) are laid-up in a mandrel (known in the arft; e.g., of the type like mold ZD-l for strips like LS-l, both described below relative to FIGS. 2D and 4 respectively) to follow a prescribed profile corresponding to the in-situ disposition of prescribed set of 12-hammer-slugs and associated pairs of bonding cavities J-l, etc., such a disposition being known in the art and further described hereinafter. Each strip C comprises a pair of spaced parallel leg portions L separated by a relatively orthogonal base portion b (e.g., legs L L' and base b comprising strip C-1). For this arrangement strips C may be understood as slit from a stock sheet of composite glass fiber resin material. A preferred such sheet is a preimpregnated uncured linear glass fabric (prepreg) material, such as that described in the following examples. Such prepreg sheets comprise a composite layer of linear glass fiber in a resin matrix, uncured, (or several such layers), preferably bonded on a support backing, such as a woven skrim layer (or layers), the latter only for handling strength.

For instance, exemplary strip LS-1 in FIG. 4 illustrates a preferred construction where a pair of such composite layers are attached on an intermediate skrim to form a unitary support (analogous to individual legs L in FIG. 2C). Such strips are taken from uncured (or semicured) stock and cured during assembly (e.g., in FIG. 2A) so that proper bonding (e.g., with slug and base) may be effected. These support strips (C) will be otherwise rather conventional, i.e., about 4 inches long (leg height being approximately a conventional l in.), about 1416 mils thick and about 80-85 mils wide. For an alternate strip construction, and method for fabrication thereof, reference may be had below to the description of other preferred strip materials, the structure of strip LS-l in FIG. 4 and the description of strip preparation including molding (cf., FIG. 2D).

For the embodiment of FIG. 2C, workers in the art may visualize known methods and implements whereby a set of U-strips (C-l, etc.) may be disposed in paral lel, separated a prescribed distance (e.g., about 15 mils, comparable to typical interslug separation), and, preferably, formed into an integral unit Sh, for instance by bonding all strips onto a common base-sheet (LB, in phantom). For instance, bases b through b may be bonded to a sheet of prepreg (or several such) or the like, for subsequent insertion into a slug-assembly jig (FIG. 2A).

This array Sh of support strips C-l through C-12 in FIG. 2C may now be inserted into a suitable jig (assembly-molding fixture) for bonding to the hammer slugs and molding of the common base in one integral operation according to the invention. Such a jig fixture M is indicated in FIG. 2A, comprising a jig body MD-2 together with an associated base BV-KC and cover CR. Jig MD will be understood as adapted for forming finished hammer module HM in FIG. 2B. Such a striparray Sh may be equivalently formed as understood in the art, such as by cutting out a U-shaped sheet of prepreg (to form legs L) or with a compression mandrel. Such a mandrel consists essentially of a U-shaped cavity notched to receive strips of the glass fiber epoxy material laid across twelve U-shaped strip-cavities (grooves) in a form block, the block being adapted to be pressure-fit into the mandrel housing to force each strip to conform to its respective cavity and thus form a flexure strip having the required thickness, dimensional tolerances, etc. These strips will, as above, preferably, be joined with a common base portion to make an integral (e.g., 12-strip) support array.

These strips may then be heat-cured, trimmed and placed (either separately, or preferably as a 12-unit array) into receiving slots in jig body MD-Z through respective slots SS communicating between upper and lower cavities CV, CV in the body. Cavities CV, CV are of uniform cross section and run the length of the structure, each being proportioned, respectively, to receive the array of slugs S-l through S-12, and to form the common base BV (FIG. 23). More particularly, base cavity CV is proportioned so that a quantity of resin may be poured therein to both form a prescribed base BV and to bond (fuse) strip bases b through b integrally therewith in the same operation, according to this feature of the invention. It will be recognized that such a bonding/molding operation is not only extremely convenient and inexpensive, but forms a very firm bond with support legs L, L since the entire intermediate, common base is fused with the common base-segment b between the legs. Cavity CV also preferably includes a groove portion BV-KC for forming a key (notch BV-K, shown in phantom in FIG. 2B and known to be conventional in the art for readily locating the slug module HM properly in the printer). Typically, base BV would be about 1.185 inches long by about 1.218 inches wide by about .400 inch thick, spanning twelve print columns (or any convenient number thereof). In prior art hammer units, such operations are very difiicult, fussy and expensive to perform and moreover not as efiective as desired, since the flexures and/or the base-bonds too often fail. Using such techniques according to the invention, I have found that modules of this type made according to the invention to have a fail-free operating life of well in excess of one hundred million cycles (approaching the optimum desired level of about three hundred million cycles, corresponding approximately to a common life-standard for the typical high-speed printer).

According to a feature of the invention, jig MD will be relieved on one (or preferably both) sides of slugcavity CV (along the plane corresponding to the positions spanned by slugs S-1 through S12, these openings being shown in phantom only, but readily understood by those skilled in the art, such as from consideration of FIG. 2B). These openings of slugs may be inserted therethrough into cavity CV so'that the slug-cavities (e.g., J-1 for slug S-1) are in registry with respective pairs of slots SS which are, in turn, adapted to receive the associated leg-supports (e.g., L L the slugs being thereby disposed in proper print-registry along cavity CV. As a means of maintaining this registry, and according to another feature of the invention, a set of eleven separating sliders SL-l (shown exemplarily) through SL-11 are provided. Sliders SL are fabricated of a prescribed uniform size for insertion between respective pairs of slugs S (as indicated exemplarily, in phantom, for SL-l in FIG. 2B). Sliders SL will be removably inserted so as to be slideable back and forth (direction of arrow SD) in cavity CV or removed entirely as desired. According to this feature of the invention, each slug SL is provided with a pair of bores (a) corresponding approximately to the diameter of the bonding cavities J in slugs S (e.g., J-l for slug S-1). The array of pairs of cavities J-1 through J-12 are kept in registry within jig MD when slugs S1 to S-12 are so disposed therein by any convenient means (not shown, e.g., conventional straps). Bores a are disposed so that slides SL-1 through SL11 may be inserted between their respective slugs with the bores in registry with adjacent bond-cavities J (the slides being held by conventional straps, clamps, by a friction-fit or the like). As a result, and according to this feature of the invention, bonding resin may now be injected into cavity CV to form the base as aforementioned, while (support-slug) bonding resin may also be injected in common down the two tubes formed by the aforedescribed twelve registered pairs of slug-cavities (pairs J1 through J-12) and through the intermediate slide-cavities a so as to form a pair of integral bonds between both sets of aligned support legs (e.g., L through L and L through L and their respective slug cavities J (and slide cavities a, also) in a single convenient operation. Now, according to this step (the resin being sufliciently set-up, or viscous, so as not to flow), the eleven slides SL are shifted so as to move bores a out of registry with cavities J sufiicient to rupture the integral bond therealong (along each of the two registeredcavity tubes). This will prevent a bond from forming between adjacent slugs and allow the separate, independent reciprocation of each slug in module HM as is well understood in the art.

Module HM now having been formed, it may be removed from jig MD, such as by removing sliders SL and sliding HM laterally (transverse the slug-length), the resinreceiving cavity CV having been conventionally lubricated for this (parting facilitated), cover CR removed, supportreceiving slots SS permitting this (e.g., slots SS made to extend the length of MD-Z to communicate outside of one or both outer sides) and so forth. The convenience of this method will be apparent, especially in terms of how easy it is to form the support/ slug bond, still providing a secure Of course, those skilled in the art will recognize that A alternate configurations other than those described in the embodiment of FIGS. 2A, 2B, 2C above may be employed within the contemplation of the invention and the appended claims. For instance, modules having somewhat more, or somewhat less, than the twelve hammers of module HM aforedescribed may be fabricated with relatively the same convenience and in the same manner. Alternatively, one may form strips C shown in FIG. 2C in other ways, such as by cutting-out (or stamping, etc.) legs L individually, or such as by folding a U-shaped web (indicated by the dotted line profile in FIG. 2C) and slicing out the gaps between adjacent leg-pairs (as aforementioned, although this method is less preferable, for instance, because the slicing operation is somewhat fussy, time-consuming and rather difiicult due to the abrasive nature of the glass). Similarly, the base BV may be otherwise formed, such as by inserting a preformed section in cavity SV to fill part or all thereof bonding this with the resin to base portions (b etc.) or the like. Again, the mold body MD-2 may be varied within the contemplation of the invention; for instance, so that the slugs and intermediate slides SL are inserted through top (vs side) openings, communicating with cavity SV', into proper registration, this registration being assured by end-notches in these entrance-openings and the like (slides SL thus being upwardly, rather than laterally, movable to rupture the common interslug-support potting). Similarly, in certain instances, it may be preferable to form slides SL to comprise a single multitined unit, all slide-tines being projected from a common base with this (ll-tined) unit being insertable as a single structure into the interslug spaces (or two such ll-tined units, one insertable from the left, the other from the right), or the like.

Moreover, where the support strips were indicated in FIG. 2C, etc., as being generally U-shaped and in an integral structure comprising a pair of legs formed to project from a common base; in certain instances, it may be preferable to form the legs separately, dispensing with all (or a portion of) the intermediate base. Thus, each leg may form a somewhat C-shaped member, after the manner of legs 103, 103' shown in FIG. 5, as part of an alternate hammer-module embodiment M. Module M will be understood to be constructed and fabricated like module HM aforedescribed except as indicated. Thus, module M comprises an array of six aligned hammer slugs 106, each having an intermediate necked-down (shank) portion 106M, and a pair of bonding cavities (similar to cavities J in FIG. 2) for receiving and bonding support elements 103, 103 which are spaced a distance S (about 15 mils). According to this embodiment (and as may be understood by those skilled in the art), the bonding resin is poured down these registering bonding cavities to form resin bonds 104, 104 between the supports and the slugs. Preferably, although it is not necessary, each support 103, 103' also includes an upper, laterally-projecting tip 103-e, 103'e with the bond-cavity in the slug being fashioned to accommodate this portion and surrounding potting portions 111, 111' being provided to bond these tips onto the slug-shanks 106-M. This will be seen to provide increased support area for bonding to the shank more firmly. The length and area as well as the size of the bonding cavities will, of course, be little more than sufiicient to provide a firm bond, preferably being cut-away to accommodate the tips 103-e, etc., as shown. Of course, base is integral with the bond to the supports (as shown) and may be formed in the same operation as the injection of support-potting portions 102, 102.

According to a subfeature of the invention, I have found that certain structural features and fabrication techniques are often preferable in providing composite support flexures of the aforementioned type. For instance, I have found it quite desirable (often critical) in certain printer applications to fashion the strips after the manner of strip LS-1 in FIG. 4. Strip LS-l comprises a pair of outer composite glass fiber resin or the like) structural layers GL-l, GL-2 bonded to an intermediate bond-layer R. For instance, layer R may comprise a skrim (web comprising a loosely cross-woven matrix of glass fibers, disposed somewhat centrally, of axis SK) impregnated with a resin suitable for bonding adherently to layers GL (e.g., during curing thereof, together). Each layer GL, in turn, may comprise a laminate, e.g., two bonded sublayers, each comprising a linear array of glass fiber filaments (sufiicient for the proposed loading and aligned for this, e.g., along loading axis VV as above). Each layer GL may also include a further sublayer for lateral-stiffening (in lateral direction L-L, orthogonal to VV) like the aforementioned composite sublayers, except having its filaments aligned a bit crosswise to loading axis VV, e.g., at a few degrees skew (such as from about l-5). This can improve lateral stability (e.g., for chain-, or train-printers), affording a modicam of lateral support and stiffening along LL.

The aforedescribed (outer-double) construction (LS- 1) has been found quite advantageous in certain cases; for instance providing slug-supports with a failure-free operating life of over fifty million impact-cycles. By contrast, an alternate double-inner construction (having two layers like GL surrounded by bonding layers R on each outer side) was vastly inferior, typically failing after a few hundred thousand cycles (perhaps because the flexing of such a strip overloaded these weaker, outer layers). I have also found that the structural filaments (on layers GL) should not be woven (or otherwise bent--e.g., a woven glass fiber mesh is entirely unsuitable).

Workers in the art will understand that it is also very important to secure a very good bond between the (resin) matrix and the filaments (glass fiber) potted therein. For this reason various coupling agent finishes will often be desirable on the filaments. Also, solid resin particles may be adhered on the continuous glass filament surfaces to roughen them somewhat, impeding lateral slippage of adjacent strands (should they happen to touch) and promoting bonding and lateral-flexing strength, (eliminating fraying, etc.).

In some cases, it may be desirable to form the glass fiber resin composite per se. This may be done according to the method of Example I as follows:

EXAMPLE I Filament.Strands of glass are provided, such as a linear glass fabric material (i.e., nonwoven, linear fibers).

Coupling agent-Coat strands with coupling agent finish.

Resin.To an epoxy resin, add about 3-5 by weight of curing agent and mix with about 5-8 parts by weight of liquid nitrile elastomer.

The finished fabric will be placed in the strip mold with its glass strands aligned along the prescribed striploading direction and the resin mix infiltrated therebetween as a strand-separating potting matrix, adapted to bond very firmly with the strands. The composite will then be cured ad lib to a satisfactory degree (e.g., about l-120 C. for about 20-45 minutes is typical).

The resultant composite strip will be observed to be quite satisfactory for printslug supports, etc., like those aforedescribed. For instance, this strip may be expected to normally exhibit a tensile strength on the order of 1600 p.s.i. and suffer elongation on the order of four to five times. The liquid nitrile elastomer additive is a resin modifier primarily intended to minimize crack-propagation tendencies (no intra-resin damage under severe tensile fatigue exposure). It is a low molecular weight copolymer of butadiene and acrylonitrile (with active sites in the form of carbon-to-carbon unsaturation distributed throughout its molecule). More particularly, it is a carboxylterminated polybutadiene (polymeric dicarboxylic acid) with acrylonitrile introduced to enhance adhesion, resin compatibility, etc. Other curing agents (reacting with the carboxyl group) may be substituted.

EXAMPLE II Filament-As Example I.

Coupling agent.-As Example I.

Resin.To the epoxy resin and elastomer of Example I, add about 6% (by weight) of curing agent, sufficient for good curing; and then cure (in the manner of Example 1).

Other appropriate additives may, of course, be used, as known in the art. For instance, a cure retardant may be desired. Viscosity may be reduced relatively conventionally, such as with a suitable plasticizer like dioctyl phthalate. Antioxidants may also be desired.

Where other resin formulations are substituted, certain desirable characteristics of the matrix material should be borne in minde.g., it should not become brittle and should have high fatigue strength and high inter-laminar shear strength (according to the anticipated stresses). Related epoxy resins may be contemplated. Whatever the resin matrix, an appropriate, compatible coupling agent will ordinarily be desired for anchoring the resin, chemically, to the smooth glass surface (which is inapt for mechanical bonding and typically hydrophilic, rather than resinophilic). Another suitable coupling agent for bonding an epoxy resin (and other thermosetting resins) to glass is an organo silane compound, such as amino ethyltriacetoxy silane (e.g., applied as a size, or finish, on the glass; and drying it there). The glass filament material is less critical; for example, a relatively weak E glass will usually be adequate (without need for a high-strength glass (e.g., S glass).

It will thus be seen that the objects of the invention such as those set forth above are efficiently obtained. Since certain changes may be made in carrying out the above method and in the construction set forth without departing from the scope of the invention, and since in some cases, certain features of the invention may be used to advantage without a corresponding use of other features, it will be understood that the foregoing descriptive matter and illustrations shall not be interpreted in a limiting sense, but only as illustrative of the best forms of the invention known in accordance with the provisions of the patent statutes.

Having now described the invention, what is claimed as new and desired to secure by Letters Patent is:

What is claimed is:

1. A method of fabricating a registerable multiunit structure so that each of a set of like aligned load members is bonded to at least one projecting elongated piece, all such pieces being like in structure and oriented so that when the load members are aligned, each piece thereon may be registered with a corresponding piece on the other load members and to thus, comprise at least one set of aligned pieces, each such piece being adapted to be bonded at one respective load-end in a respective bore portion of the associated load member to project therefrom in prescribed fixed relation, said method comprising the steps of:

aligning said load members in spaced relation along a prescribed reference plane, so that al corresponding bore portions lie in registry along at least one bore locus, there being one such locus for each registered set of bore portions; and disposing each said piece to present its bondable load-end projecting into prescribed orientation with a respective bore portion and maintaining all these members and so-oriented pieces so aligned for assembly; then, enclosing each said bore locus with mold-closure means so as to form a respective tunnel for receiving fusible material, while maintaining said members and said pieces fixed in said prescribed aligned relation; then, introducing fusible bonding material into each said tunnel to fill it, said material being adapted to bond to the confronting surfaces of said pieces and said load member, there, and thereby finnly join these together in said prescribed relation; then, allowing said material to reach a viscous nonfiowing condition; and removing said tunnel-forming closure means and rupturing said nonfiowing material portions between respective bore portions along each said tunnel so that each so-formed unit, comprising a load member and one or more projecting pieces, may be manipulated independent of the other units; said step of enclosing each said bore locus including the steps of introducing separating means between each said load member to establish the said spacing therebetween at least adjacent each said tunnel-forming bore portion, having provided each separating means with a bore portion corresponding to each respective tunnel it will adjoin, and aligning each said bore portion to register with this tunnel portion and cooperate in defining it; said step of rupturing said nonfiowing material portion including the step of displacing each said separating means after said material has reached viscous nonfiowing condition to effect said rupturing. 2. The method as recited in claim 1 wherein are also provided the steps of:

arranging the base end of each said piece, opposite said load-end, to assume and maintain a prescribed orientation with respect to said respective load member; forming an enclosure about coplanar portions of all the so-oriented base ends to define a mold cavity for fabricating a common base member mounting all said pieces so as to, alone or together with a cooperating piece, provide a pivot support for the respective load member bonded to said base member; and filling said cavity with fusible base-forming ma terial to so establish said common-base mounting. 3. The method as recited in claim 2 wherein said align ing includes the steps of:

arranging a prescribed set of hammer-slugs in prescribed registration to comprise said load members, each such slug having a pair of bores defining said bore-portions; and wherein said other steps comprise introducing a similar slug-supporting fiexure strip into each said slug-bore and aligning the' two sets of bore and associated aligned strips into registry to form two such tunnels; and introducing fusible material to fill each said tunnel and both said strips and respective slugs and to form said common base member. 4. The method as recited in claim 3 wherein said rupturing step comprises:

providing a set of like separator blocks, each having a width to define said interslug spacing and each having a pair of bores adapted to be registered with the corresponding slug-bores to cooperate in defining said mold tunnels, said blocks also being adapted to be readily displaceable out of slug-bore registry sufficient to rupture the resin-formed bond along each tunnel between adjacent slug bores and thus efficiently separate the hammer slugs for independent actuation and the like.

5. The method as recited in claim 4 wherein each said support strip is fabricated to comprise an elongate composite structure including high-modulus filaments potted in a relatively weak, elastic matrix material, this material being selected to have a prescribed diiferent elasticity from said filaments.

6. The method as recited in claim 5 wherein each said strip structure is material-selected and fabricated to comprise at least one layer of glass fiber strands aligned along the elongate axis and wherein said potting material comprises a compatible thermosetting resin, said glass and resin materials being prepared so as to bond together very firmly.

7. The method as recited in claim 6 wherein each said glass fiber-resin strip is material-selected and fabricated to comprise at least one layer of linear nonwoven glass fibers aligned along the prescribed loading direction for said strip and matrix material comprising an epoxy resin arranged to bond very firmly with said glass fibers and formulated to exhibit little crack-propagation or brittleness and exhibit high fatigue strength and high interlaminar shear strength in the contemplated environment; or composite materials functioning equivalently.

8. The method as recited in claim 7 wherein said glass fibers are coated with a coupling agent; and wherein said resin is formulated to comprise a suitable epoxy resin prepared with an appropriate curing agent, an anticrack additive, and like additives.

9. The method as recited in claim 8 wherein said matrix resin is formulated from an epoxy resin together with a compatible curing agent and a few parts by weight of a liquid nitrile elastomer or like anti-cracking additive.

10. The method as recited in claim 6 wherein said glass fiber-resin strip each comprises an outer-double construction comprising a pair of outer glass fiber-resin strips bonded firmly to an intermediate support-bonding matrix including a loosely woven web of glass fibers and a surrounding matrix of bonding resin.

11. The method as recited in claim 10 wherein each said outer composite-resin layer comprises a linear array of filaments arrayed in one or more layers aligned along a common prescribed filament axis, this axis being skewed on the order of a few degrees from the contemplated strip loading axis, these filaments being potted adherently in an epoxy resin type matrix.

12. The method recited in claim 3 wherein said slugsupporting strip pairs are provided by disposing the strips in two sets, with the strips in each set aligned along a reference strip-plane in prescribed spaced relation, corresponding to prescribed interslug spacing and therealong enabling each set to be registered along an associated tunnel, and then bonding each set of strips to a common backing web; thereafter, injecting each strip array as a unit so the respective load-ends of the strips register in their associated bores.

13. The combination as recited in claim 12 wherein the two aligned sets of strips are arranged with their reference planes parallel and in prescribed spaced relation corresponding to the interbore spacing along a slug; and wherein the base ends of all strips, opposite their slugbonding ends, are bonded in common to a single base web, comprising said backing web, to thereby form a single U-shaped unit for presenting both pairs of strip sets into the associated pair of tunnels conveniently.

References Cited UNITED STATES PATENTS 3,334,409 8/1967 Shneider 264275 X 3,413,713 12/1968 Helda.

ROBERT F. WHITE, Primary Examiner A. M. SOKAL, Assistant Examiner US. Cl. X.R.

UNITED sTATEs PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,523,992 August 11, 1970 Charles Bickoff It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 12, line 8, "a1" should read H all line 24, after "prescribed" insert fixed Column 14, line 5, after "composite" insert glass fiber same line 5, after "of" insert glass fiber a Signed and sealed this 23rd day of March 1971.

(SEAL) Attest: Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

